Heretofore, interconnections formed by the damascene process (so called “damascene interconnections”) have been widely used for bit lines and the like. The damascene interconnections are formed in grooves made in an insulating film, embedding an interconnection material in the grooves and then flattening the top of the insulating film by
Chemical Mechanical Polishing (CMP).
In recent years, shrinking of semiconductor devices has decreased the distance between two neighboring bit lines (or between a bit line and its neighboring bit line contact). In addition, due to such shrinking, a bit line and its neighboring bit line contact are misaligned from each other in some cases. In these cases, a leakage current may flow between the two neighboring bit lines, or between the bit line and its neighboring bit line contact. The short-error occurrence rate will increase, because a breakdown voltage between the two neighboring bit lines, or between the bit line and its neighboring bit line contact, may be lowered.
Meanwhile, a stopper film for stopping a process in order to control the depth of each damascene interconnection is sometimes formed. In such cases, for instance, a silicon nitride film is used as the stopper film. For this reason, the silicon nitride film is present between each two neighboring bit lines, or between each bit line and its neighboring bit line contact.
The presence of the silicon nitride film between the two neighboring bit lines or between the bit line and its neighboring bit line contact increases a leakage current which flows via this silicon nitride film or via an interface between the silicon nitride film and the insulating film under the silicon nitride film. In addition, the presence of the silicon nitride film increases the short-error occurrence rate due to dielectric breakdown.